applied sciences Article Study of Eco-Friendly Belite-Calcium Sulfoaluminate Cements Obtained from Special Wastes Antonio Telesca 1 , Thomas Matschei 2 and Milena Marroccoli 1, * 1 Scuola di Ingegneria, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy; [email protected] 2 Institute of Building Materials Research, RWTH Aachen University, Schinkelstr. 3, D-52062 Aachen, Germany; [email protected] * Correspondence: [email protected] Received: 15 November 2020; Accepted: 30 November 2020; Published: 3 December 2020 Abstract: Belite-calcium sulfoaluminate (BCSA) cements are special binders obtained from non-Portland clinkers; they have become increasingly more important due to their environmental impact during the manufacturing process compared to Portland cements, such as lower energy consumption and CO 2 emissions. The aim of this paper was to assess the possible use of titanogypsum (T) and water potabilization sludge (W) to reduce the amount of natural raw materials (natural gypsum and clay, respectively) used in the production of BCSA cements. Three BCSA clinker generating raw mixes, containing T and/or W, and a reference mix based only on natural materials (limestone, clay, bauxite and natural gypsum) were heated in an electric furnace at temperatures ranging from 1200 to 1350 ◦ C. Quantitative X-ray diffraction (XRD) analysis of the burnt products showed high conversion of reactants towards the main hydraulically active BCSA clinkers components (C 2 S and C 4 A 3 $), particularly at temperatures of 1300 and 1350 ◦ C. Isothermal calorimetric measurements, differential thermal–thermogravimetric and XRD analyses as well as porosimetric measurements showed that all BCSA cements, from mixing the clinkers (at optimum temperatures) with commercial anhydrite, exhibited similar hydration behavior. Keywords: sustainability; titanogypsum; water potabilization sludge; synthesis; belite-calcium sulfoaluminate cements; hydration 1. Introduction The cement industry consumes huge amounts of natural raw materials and fuels, mainly fossil fuels and pet coke. It is one of the main contributors to climate change due to greenhouse gas emissions, mainly CO 2 . In 2018, global cement production was about 3.99 billion tonnes, accounting for about 8% of all anthropogenic carbon dioxide emissions [1]. Ordinary Portland cement (OPC), a blend of clinker (about 95%) and gypsum, is the most used binder in the world. OPC clinker is usually obtained by heating a mixture (raw meal) of limestone (L, 80% by mass) [2] and clay (C) in a rotary kiln at about 1500 ◦ C. According to [3], about 0.83 kg of CO 2 is released from the production of 1 kg of OPC; it is generated from both L thermal decomposition (about 60% of the total CO 2 emissions) and fuel combustion [4,5]. To reduce its carbon footprint, the cement industry is exploring how to manufacture OPC with less impact on the environment through a switch to: (I) alternative fuels, (II) reduction in thermal energy demand, (III) use of non-carbonated CaO sources instead of L, (IV) decrease in clinker to cement ratio, (V) application of carbon capture and storage technologies to cement plants [6], and (VI) development of low-CO 2 non-Portland binders (e.g., alkali-activated, Mg-based cements, calcium sulfoaluminate (CSA) and belite–CSA (BCSA) binders) [7–25]. Appl. Sci. 2020, 10, 8650; doi:10.3390/app10238650 www.mdpi.com/journal/applsci
Study of Eco-Friendly Belite-Calcium Sulfoaluminate Cements Obtained from Special Wastes
May 05, 2023
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